1. Technical Field
The present invention relates to a plating apparatus and particularly to a plating apparatus used in the semiconductor fabrication process for forming a metal plating on a substrate, such as a semiconductor wafer or the like.
2. Description of Related Art
The plating process is used frequently in semiconductor fabrication process to form wiring or films on a substrate. FIG. 1 shows the construction of this type of plating apparatus. As shown in the drawing, the plating apparatus comprises a plating section 1 and a control section 2. The plating section 1 includes a plating bath 1-2. The control section 2 includes a replenishing tank 2-2 and a replenishing tank 2-3.
The plating bath 1-2 accommodates a plating solution 1-1, a substrate 1-4 mounted on a wafer holder (not shown) in the plating solution 1-1, and a soluble anode 1-3 disposed in the plating solution 1-1 opposite the substrate 1-4. A power source 1-5 is connected between the substrate 1-4 and anode 1-3. The plating section 1 also includes a pump 1-6 and a temperature regulator 1-7. The pump 1-6 supplies the plating solution 1-1 to the temperature regulator 1-7. The temperature regulator 1-7 adjusts the plating solution 1-1 to a temperature optimal for the plating process and returns the plating solution 1-1 to the plating bath 1-2.
The replenishing tank 2-3 accommodates a plating solution 2-5, such as an aqueous solution primarily comprising predetermined concentrations of CuSO4-5H2O. The plating solution 2-5 is supplied to the plating bath 1-2 by the pump 2-7 through the pipe 3. The replenishing tank 2-2 accommodates an additive solution 2-4, and the solution 2-4 is supplied to the plating bath 1-2 by the pump 2-6 through the tube 4. When the apparatus is first powered on, new plating solution 2-5 is introduced into the plating bath 1-2. During plating operations, an analyzing apparatus (not shown) analyzes the composition and concentration of the plating solution 1-1 from the plating bath 1-2. Based on these analyses, the additive solution 2-4 or the plating solution 2-5 is supplied from the replenishing tank 2-2 or the replenishing tank 2-3 in order to maintain the composition and concentration of the plating solution 1-1 at predetermined values.
When the power source 1-5 supplies a plating current between the substrate 1-4 and anode 1-3, metallic ions, such as Cu2+ are emitted from the soluble anode (for example, a phosphorus copper electrode) 1-3 and deposited on the surface of the substrate 1-4 to form a metallic plating film. It is necessary to replace the anode 1-3 periodically because the anode 1-3 is consumed as it emits metallic ions into the plating solution 1-1.
The plating solution used in this plating apparatus contains metallic ions that are deposited on a member to be plated. Sometimes the deposited metal is transferred or diffused. Further, when the plating solution or mist from the solution is vaporized, crystals are deposited, generating solid particles. This metallic deposited matter and the crystalline particles are causing contamination for clean rooms, semiconductor wafers, and circuit materials.
In the semiconductor fabrication process, metallic plating is embedded in fine wire channels and the like formed in the surface of semiconductor wafers. From a process control standpoint, it is advantageous to conduct these plating processes in a clean room. However, by installing the plating apparatus comprised of the plating section 1 and control section 2 in a clean room, the replenishing tank 2-2, replenishing tank 2-3, and liquid analyzer (not shown) must also be disposed in the clean room by association. This raises the problem of managing the above-described contamination during maintenance operations.
FIG. 2 shows an example construction of a plating apparatus employing a conventional insoluble anode. As shown in the drawing, the plating apparatus comprises a plating section 1 and a control section 2. The plating section 1 includes a hermetically sealed plating chamber 1-24 and a regulating tank 1-31. The control section 2 includes replenishing tanks 2-2, 2-3, 2-17, and 2-23. The plating chamber 1-24 is divided into an anode chamber 1-24a and a cathode chamber 1-24b by an ion exchange membrane 1-25. An insoluble anode 1-23 is disposed in the anode chamber 1-24a, while a substrate 1-4 is disposed in the cathode chamber 1-24b and opposes the anode 1-23 across the ion exchange membrane 1-25.
The regulating tank 1-31 is divided into an anode chamber 1-31a and a cathode chamber 1-31b by an ion exchange membrane 1-27. A soluble anode 1-28 is disposed in the anode chamber 1-31a, while a cathode 1-29 is disposed in the cathode chamber 1-31b and opposes the anode 1-28 across the ion exchange membrane 1-27. A power source 1-33 is connected between the anode 1-28 and cathode 1-29. The anode chamber 1-31a accommodates plating solution 1-1, while the cathode chamber 1-31b accommodates electrolytic solution 1-22. When the power source 1-33 applies a predetermined voltage between the anode 1-28 and cathode 1-29, the anode 1-28 dissolves and emits metallic ions.
A pump 1-14 supplies the plating solution 1-1 from the anode chamber 1-31a to the cathode chamber 1-24b via a tube 1-20 and a filter 1-16 provided on the tube 1-20. A pump 1-15 supplies electrolytic solution 1-22 from the cathode chamber 1-31b to the anode chamber 1-24a via a tube 1-21 and a filter 1-17 provided on the tube 1-21. The apparatus is also configured to return the electrolytic solution 1-22 from the anode chamber 1-24a and the plating solution 1-1 from the cathode chamber 1-24b to the cathode chamber 1-31b and anode chamber 1-31a, respectively.
Hence, the power source 1-5 applies a predetermined voltage between the anode 1-23 and substrate 1-4, supplying a current from the anode 1-23 to the substrate 1-4. The current forms a metallic film on the surface of the substrate 1-4. Metallic ions such as Cu2+ ions consumed during the plating process in the plating chamber 1-24 are replenished from the regulating tank 1-31.
When using an insoluble electrode for the anode 1-23 as described above, there is no need to replace the electrode. Therefore, maintenance work can be reduced. However, the anode 1-28 in the regulating tank 1-31 must be replaced. Further, O2 gas is released from the region near the anode 1-23 and H2 gas is released from the region near the cathode 1-29. From a safety standpoint, it is not desirable for both gases to be released in the same clean room.
In the plating apparatus having the construction described above, a lot of the washing solution is discharged when washing the substrate 1-4 after the substrate is plated. Hence, a lot of washing solution and pure wafer are consumed, particularly when the substrate 1-4 to be plated is, for example, a semiconductor wafer for fabricating a semiconductor device. Further, since the washing solution contains plating solution, it is necessary to process the solution to remove metallic ions and the like, which can place a great burden on the wasted water processing equipment. The same problem exists when processing wasted plating solution that has been degraded.
Therefore, an effective method to reduce the overall load on the equipment is to provide the plating apparatus with functions to recover wasted plating solution and to process wash water. Such functions can perform specialized functions by themselves to enable the plating apparatus to process the plating solution and solution containing plating solution. Here, great benefits can be obtained by providing functions to regulate the plating solution, to remove metallic ions from the wash water after processing, and to re-regulate and recover wasted plating solution in a separate room from the room housing the plating section 1, which is required to be extremely clean. From a maintenance standpoint, it is very beneficial to manage the plating solution, process the plating solution, and process the wash water by the plating apparatus itself. However, a conventional plating apparatus has not been developed to perform these functions.